A light emitting diode (LED) is eco-friendly. In addition, since the LED has a response speed of several nano-seconds to respond at a high speed, the LED is effective in a video signal stream.
In addition, the LED allows impulsive driving, and has more than 100% of color reproducibility. In addition, brightness and a color temperature may be arbitrarily changed by adjusting the quality of light of a red, green, or blue LED.
In addition, the LED, which is an eco-friendly light source having no mercury differently from other light sources, has been spotlighted as a next-generation light source used in a backlight unit (BLU) for a portable phone, a BLU for an LCD TV, a lamp for a vehicle, and a typical lamp.
Accordingly, an incandescent light used as a main light source for lighting and having a low-power efficiency characteristic or a fluorescent light having an environmental waste such as mercury has been substituted with the LED lamp.
A lamp of a type similar to the fluorescent light uses a ballast (electric transformer). When the lamp is substituted with the LED lamp, a conventional ballast is used for the LED lamp without change.
In the case of the LED lamp using the ballast (electric transformer) similarly to the conventional circuit configuration, the output voltage of the ballast becomes input voltage of a power supply unit (PSU) of the LED lamp without change.
Accordingly, the compatibility between the ballast and the PSU may be varied depending on the manufactures of the ballast and the LED lamp, thereby causing the erroneous operation of the LED lamp or the ballast.
Accordingly, the compatibility between the PSU including a switching mode power supply of the LED lamp and the ballast is important.
In particular, since the ballast is configured in the structure of an inverter, the ballast outputs a significantly swift waveform. In the case of a conventional PSU using the output as input voltage after rectifying the output, the compatibility with the output from the ballast may be lowered.
In addition, the operating voltage of the PSU of the LED lamp is insufficient, so that the PSU may be erroneously operated. When the PSU is erroneously operated, phenomenon such as flicker and noise may occur.